Addition alloys

ABSTRACT

DIRECTED TO ALLOYS WHICH ARE PARTICULARLY SUITABLE FOR THE INTRODUCTION OF MAGNESIUM INTO MOLTEN IRON AND WHICH CONTAIN IN WHICH PERCENT ABOUT 5% TO 15% NICKEL, ABOUT 5% TO 14% MAGNESIUM, ABOUT 34% TO 60% SILICON, ABOUT 0.5% TO ABOUT 3% OF A RARE EARTH METAL, UP TO ABOUT 4% CALCIUM, UP TO ABOUT 2% CARBON, UP TO ABOUT 10% MANGANESE, UP TO ABOUT 10% COPPER, THE BLANCE BEING ESSENTIALLY IRON, IN AN AMOUNT LESS THAN ABOUT 50%.

United States Patent U.S. (175-122 6 Claims ABSTRACT OF THE DISCLOSURE Directed to alloys which are particularly suitable for the introduction of magnesium into molten iron and which contain in weight percent about to 15% nickel, about 5% to 14% magnesium, about 34% to 60% silicon, about 0.5 to about 3% of a rare earth metal, up to about 4% calcium, up to about 2% carbon, up to about manganese,up' to about 10% copper, the balance being essentially iron, in an amount less than about 50%.

This invention is directed to alloys and, in particular, to addition alloys suitable for the introduction of magnesium into molten iron.

The introduction of magnesium into molten iron is widely known and practiced for the production of spheroidal graphite cast iron in which the graphite is rendered spheroidal by means of retained magnesium. To insure that the'graphite formed in the cast iron, either on solidification, or during a graphitizing heat treatment, is spheroidal, generally requires a retained magnesium content of up to about 0.1%, e.g., from 0.02% to 0.08%.

As is well known in the art, the direct addition of magnesium metal to molten metal is generally not practiced because of its high vapor pressure of about 6 to 10 atmospheres at the usual temperature of treatment, for example, 1400 C. to 1500 C.; at these conditions, there would be a violent reaction. Several-processes have been developed to add magnesium safely to the molten metal, one of which is the use of addition alloys.

Of the addition alloys employed at present, those containing nickel are extremely elfective in moderating the violence of the reaction between the magnesium and molten iron. It has generally been found however, that large percentages of nickel, e.g., 60% to 70% or more are necessary in order that a high alloy efliciency may be obtained. The utility of an addition alloy for introducing magnesium into molten metal is measured in terms of its efficiency and it is essential that a high alloy efiiciency be obtained because at lower efiiciencies more alloy must be added to the molten metal to introduce the desired quantity of magnesium. The introduction of large quantities of addition alloy to the melt may cause additional problems because of excessive cooling and can result in an increased tendency for the occurrence of dross and other casting defects. As in all commercial processes, it is also essential that the additional alloys be economical to use.

It is an object of the'present invention to provide addition alloys for use in introducing magnesium to molten iron which possess high cost efliciencies, that is, optimum magnesium recovery coupled with lowest addition alloy cost.

Generally speaking, the present invention is directed to alloys containing (in weight percent) about 5% to about nickel, about 5% toabout 14% magnesium, about 34% to about 60% silicon, about 0.5% to about 3% of a rare earth metal, up to about 4% calcium, up to about 2% carbon, up to about 10% manganese, up to about 10% copper, and the balance essentially iron, the iron content being less than about 50%.

Patented Aug. 13, 1974 In carrying the invention into practice, a preferred compositional range comprises about 8% to about 15% nickel, about 9% to about 13% magnesium, about 34% to about 50% silicon, about 1.5% to about 2.5% of a rare earth metal, about 1.5% to about 2.5% calcium, the balance being essentially iron.

A more preferred alloy comprises about 9% to about 13% nickel, about 9% to about 13% magnesium, about 38% to about 45% silicon, about 1.5% to about 2.5 of a rare earth metal, about 1.5 to about 2.5 calcium, up to about 1% carbon and the balance essentially iron.

As described above, the utility of an addition alloy for introducing magnesium into molten metal may be measured in terms of its efliciency, which may be defined as follows:

Efficiency (percent) Mg recovery (percent) XMg content of alloy (percent) where:

Mg recovery (percent) It is essential that the nickel content be at least 5% for acceptable magnesium recovery and consequently, acceptable alloy efficiency. Nickel contents below 5% in the alloy result in sharp reduction of these properties therein, while nickel contents exceeding about 15% add to the cost of the alloy, For maximum cost-efliciency, the preferred nickel content is at least 8% but less than about 15 and most preferably is from 9% to 13%.

Alloys containing less than about 5% magnesium provide excellent recovery values but, because there is a low magnesium content, the efliciency is poor. If the alloys contain more than about 14% magnesium, undesirably increased reactivity may be experienced on addition of the alloy to molten iron resulting in a low magnesium recovery and hence, inadequate efiiciency. For optimum efficiency a magnesium content of from about 9% to about 13% is preferred.

Silicon is essential in the alloy to ensure that the melting point of the alloy is low compared with the normal temperature encountered in handling molten iron in the foundry. If the rnelting point of the alloys is high, e.g., about 1450 C., the alloys are difiicult to produce and difiicult to melt in the molten iron to which they are added. The presence of silicon in the alloy in amounts from about 34% to about 60% reduces the melting point of the alloy to a temperature which is low in relation to the usual handling temperature of molten iron in the foundry and, in addition, results in the need for a smaller amount of ferro-silicon graphitizing inoculant, which is commonly employed as a late addition in the manufacture of spheroidal graphite iron. However, at higher pouring temperatures, for example, 1480 C. and above, the magnesium recovery tends to decrease at high silicon levels. For this reason and for greater ease of manufacture it is preferred that the silicon content of the alloy be maintained from about 34% to about 50%, and more preferably, from about 38% to about 45 The presence of rare earth metals in the alloy raises the magnesium recovery of the alloy. The rare earth metals are also beneficial in offsetting the eifect of incidental elements which may be present in the base charge and which may interfere with the formation of spheroidal graphite. One or more of the rare earth elements may be added, for example, in the form of Mischmetal, in an amount of at least 0.5%. The rare earth metal content of the alloy can be extended up to about 3% but at about this level and above no additional benefits are conferred. It is most preferred that the total rare earth metal content be from about 1.5% to about 2.5%.

Calcium in the alloy also contributes to magnesium recovery. For this purpose at least 0.5% may be employed in the alloy, but amounts of calcium in excess of about 4% provide no further benefits. Calcium also produces the beneficial effect of reducing the violence of the addition reaction. It is most preferred that the content of calcium in the alloy be from about 1.5% to about 2.5% or about 3%.

Carbon may be present in the alloys in amounts up to about 2%. It is believed that this element confers the advantage of reducing the violence of the reaction when the alloys are added to molten iron. A range of about 0.1% to about 1% is beneficial. The alloy may also contain up to about 10% manganese and up to about 10% copper without adversely affecting their general properties. It is preferred however, that both manganese and copper contents not exceed about The balance of the composition, up to about 50%, is iron, including small amounts of impurities. The presence in the alloy of iron exceeding about 50% can lead to an excessively high alloy melting point, which causes addition alloy production and melting difiiculties.

The nickel-containing alloys of the invention are characterized by the presence of three phases, namely a silicon-magnesium phase in a matrix comprising iron-silicon and nickel-silicon phases. Electron microprobe analysis of the silicon-manganese phase revealed a high silicon to magnesium ratio of 8.1 :1 by weight.

The alloys contemplated in the present invention may be processed following normal operating procedures. They may be readily added to an iron or other molten melt either by throwing the alloy onto the melt or by placing the alloy in an empty vessel and pouring the melt onto it. For best results, it has been found that a method of addition known as the sandwich method is the most ad vantageous. In this method, the bottom of a ladle is built up over approximately half its area, for example, by cm. The addition alloy is then placed against the ledge thus formed and covered with mild steel clippings, which usually comprise about 2% by weight of the metal to be treated. The melt is then tapped onto the platform and allowed to flow over the clippings and addition alloy.

In order to give those skilled in the art a better understanding of the invention, the following examples are given:

TABLE I Composition (percent) Rare Alloy Ni Mg Si earth Ca 0 Al Fe 1 11. 2 9. 7 38. 3 2. 16 2. 2 0.44 Hal. 2 l1. 4 10. 0 34. 8 2. 35 3. 0 0. 56 Bal. 3 10. 95 11. 0 49. 5 2. 4 2. 8 0. 19 Bal. 4 6. 0 6. 9 42. 1 2. 16 2. 1 0.21 Bal. A Bal. l5. 9 0. 46 1. 5 B 10.7 47. 4 l. 16 0. 096 1 0 42. 0

Addition alloys 1 to 4 were then employed in the production of 8.6. iron by the sandwich method. A charge of pig iron containing 3.8% carbon, 1.5 silicon, 0.1% manganese, 0.025% phosphorus and 0.01% sulfur was melted in a 100 kg. basic HF furnace for use with each addition alloy and the silicon content of the melt Was adjusted by the addition of ferro-silicon. The temperature was raised 1450 C., a small addition of manganese was made and the melt was poured at 1450 C. into a ladle containing the addition alloy. The addition alloy (0.8% by weight of the total melt) was placed against a shelf in a ladle and covered with mild steel clippings (2% by weight of the total melt), and the molten iron was poured onto the shelf. Finally the melt was inoculated with ferrosilicon. Spheroidal graphite iron was produced in a similar manner using Alloys A and B. One 30 mm. x 35 mm. x 165 mm. keel block was cast from each melt together with one analysis sample. The compositions of the spheroidal-graphite irons are given in Table II together with performance data calculated for each of the alloys.

TABLE II Alloy performance S.G. iron composition,

percent M Alloy (percentg (percent) Mg recovery efliciency EXAMPLE II Alloy performance tests similar to the one described in Example 1, except that the pouring temperature is 1480 C., were conducted using Alloys 3 and B, described hereinabove in Table I, and Alloy 5 which contained 10.6% nickel, 11.2% magnesium, 38.2% silicon, 2.7% rare earth metal, 1.24% calcium, 1.12% carbon and the balance essentially iron. The data are given in Table III.

TABLE III Alloy performance S.G. iron Addi- Amount composition, percent Mg Alloy tion added, (percent (gircent) Test No alloy percent Si Mn N1 Mg recovery e ciency S content before treatment was 0.006% for Test N0. 1, 0.015% for Test No. 2 and 0.025%

for Test No. 3

EXAMPLE I The addition alloys (1 to 4) of the compositions shown hereinbelow in Table I were all prepared in a basic HF induction furnace by adding the various elements to a base iron-silicon melt maintained at 1150 C. Quiescent melting of these additions was obtained by plunging them through a cover of crushed graphite. After the additions the temperature was raised to about 1240 C. and the graphite cover removed. The melt was then tapped into metal slab molds, 30 cm. and 5 cm. thick. Alloys A and B are not in accordance with the invention.

sium phases, the proportion of the silicon-magnesium phase being appreciably less than in Alloy No. 1 (9.7% magnesium and 38.3% silicon) and the ratio of silicon to magnesium within this phase being 0.9:1. The magnesium recovery value obtained for the latter alloy under the conditions employed in Example I was only 26.7%, compared with 57.2% for Alloy No. 1 the structure of which was found to comprise a silicon-magnesium phase in a matrix of iron-silicon and nickel-silicon phases, the silicon-magnesium phase having a silicon to magnesium ratio of 8.1:1. These results suggest that the magnesium recovery increases with an increasing silicon to magnesium ratio in the silicon-magnesium phase of the addition alloy.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. An alloy consisting essentially of about 5% to about 15% nickel, about 5% to about 14% magnesium, about 34% to about 60% silicon, about 0.5% to about 3% rare earth metal, about 0.5% to about 4% calcium, up to about 2% carbon, up to about manganese, up to 6 about 10% copper and the balance essentially iron, with the iron less than about 2. An alloy in accordance with claim 1 wherein the carbon does not exceed about 1%, the manganese does not exceed about 5% and the copper does not exceed about 5%.

3. An alloy in accordance with claim 1 wherein the rare earth metal is in the form of Mischmetal.

4. An alloy in accordance with claim 1 wherein the nickel is about 8% to about 15%, the magnesium is about 9% to about 13%, the silicon is about 34% to about 50%, the rare earth metal is about 1.5 to about 2.5% and the calcium is about 1.5% to about 2.5%.

5. An alloy in accordance with claim 4 wherein the nickel is about 9% to about 13% and the silicon is about 38% to about 45%.

6. An alloy in accordance with claim 5 wherein the carbon does not exceed about 1%.

References Cited UNITED STATES PATENTS 3,295,963 1/1967 Galvin l22 3,033,676 5/1962 Cox 75l22 3,304,174 2/ 1967 Ototani 75l22 3,715,206 2/1973 Komatsu 75l22 HYLAND BIZOT, Primary Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. I 3,829,311 DATED August 11, 1974 1 JOHN WILLIAM GRANT and GORDON JOHN cox It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 59, for "additional" read -addition-.

Column 3, line 30, for "manganese" read --m agnesium-.

Column 4, line 18, after "raised", insert --to--.

Column 4, line 57, for "Amount" read -Amounts'-.

Signed and Sealed this A ttest:

RUTH C. MASON C. MARSHALL Arresting Officer DANN ommr'ssiuner ujlarenls and Trademarks 

